It is a common occurrence to see an unsightly oil slick or trash floating in a roadside stream. The EPA has identified improvement of the quality of water discharges as a priority. The Clean Water Act mandates action for many communities. Several reports have recommended the use of hoods to cover outlet pipes in liquid-separating structures to improve storm water discharge quality. A report surveying environmental practices of seventy eight communities bordering the Long Island Sound (Natural Resources Defense Council 1998), specifically recommends using hoods to screen out floatable debris. Few communities currently follow this recommendation. The need for the separation of mixtures of liquids with different specific gravities is frequently encountered not only in such urban environments but also in various industries where oil spills occur. Conventional drainage systems control the surface area on which oil and debris fall by enabling these impurities to be collected in a liquid-separating system which is, at least partially submerged in the ground.
Many types of equipment and processes have been suggested in the past for separating liquid mixtures. Most of these methods have been based on the principle of differential specific gravity separation. The liquid mixture, which usually is waste water, flows slowly through an elongated path in a liquid-retaining structure, such as, for example, a basin. The matter to be collected is usually oil and floatable debris, both of which accumulate on the surface of the wastewater. As the wastewater passes through the basin solids carried by the wastewater accumulate on a bottom of the basin. These solids include solid debris with specific gravity greater than the wastewater's specific gravity and are too large to be suspended in the wastewater and very fine particles which are suspended in the wastewater but tend to settle to a bottom given time or a slowdown of liquid flow in the basin.
U.S. Pat. No. 5,505,860 discloses a rather typical structure of a separator wherein separation is promoted by a planar baffle plate extending across an interior of a trap body. The baffle plate retains grease on an upstream side permitting flow under the planar baffle plate to a downstream side. An outlet fitting extends upward from below to permit filtered water to exit from the trap body.
U.S. Pat. No. 4,832,846 discloses a septic tank baffle for mounting over an outlet port in a septic basin. The baffle includes a conduit terminating below the liquid level and an angled flap directing flow into the conduit from below the baffle. The conduit is provided with an open back side for mounting toward a basin wall so that there are top and bottom open ends with a front side of the baffle being formed with a plurality of walls which are joined together to form a trough.
U.S. Pat. Nos. 3,904,524, 5,505,860, 5,433,845 disclose different variations of baffle plates designed to improve separation of a liquid mixture.
However, a disadvantage of the devices disclosed in these latter patents is a complicated structure including a plurality of separating partitions. As a consequence, maintenance of submerged liquid-separating systems is, in general, more difficult.